The method relates to a method for the orientation of liquid crystals in liquid crystal displays (LCD), in which a liquid crystal layer is tightly enclosed hermetically between two transparent electrodes and at a inner electrode surface of which an orienting layer for the specific spatial orientation of the liquid crystals (LC) is linked by a chemical bond.
In any LCD, the liquid crystal, in the unstressed state, must have a specific starting orientation, which is as heat resistant as possible and has a long operational life. This starting orientation may be obtained, for example, by means of depositing vapors at an angle under vacuum on the transparent electrodes. SiO.sub.x, C, Au, Al.sub.2 O.sub.3 and TiO.sub.2, as well as organic compounds, are used for this purpose. When organic compounds are applied, the bond of the orienting layer to the substrate is not assured. In particular, this method is not suitable for the orientation of liquid crystals on large substrate surfaces, since the uniformity of the vapor deposition angle on the substrate surface no longer is present. For this purpose, vapor-deposition facilities with a large diameter would be required in order to have a sufficient distance between the vaporization source and the substrate. To achieve a particular tilt angle between the liquid crystal and the substrate surface, a double vapor deposition at an angle is even required.
The application of organic orienting layers on the transparent electrodes with the necessary, subsequent mechanical processing, has gained international acceptance. For example, silane compounds of the X.sub.n SiR.sub.4-n type (see German Offenlegungsschrift No. 2,635,630), hydrocarbon polymers such as polyvinyl alcohol (see German Offenlegungsschrift No. 2,406,350), or heat-resistant polyamides by a screen-printing method (see U.S. Pat. No. 4,278,326), by photoresist methods (see German Offenlegungsschrift No. 2,931,259), or by dipping methods with subsequent heating (German Auslegeschrift No. 2,638,091), are applied in this manner. Colored orienting layers, obtained by admixing dyes (for example, German Offenlegungsschrift No. 3,016,396), or by coupling reactive dyes to the orienting layer (as described in DD Pat. No. 221,024), are also known.
The orientation of smectic liquid crystals by vapor deposition at an angle and under vacuum, or by means of hydrocarbon polymers, is described in German Offenlegungsschriften Nos. 3,443,011 and 3,502,160. A permanent bond between the polymeric orienting layer and the substrate surface of the type described in DD Pat. No. 218,195 and U.S. Pat. No. 4,472,028, as a prerequisite for a time- and temperature-independent qualitative LC orientation, is not taken into consideration in these patents.
The teachings of German Offenlegungsschriften Nos. 3,513,437, 3,427,597 and 3,508,169, with regard to the orientation of smectic LC, all relate to the transfer of known methods to the orientation of nematic LC on smectic liquid crystals. All previous methods for the orientation of liquid-crystalline molecules are based on characteristically deforming the surface geometry of the substrates by vapor deposition under vacuum, mechanically processing an inorganic or organic surface film, hydrophobizing and hydrophilizing, so as to give the LC molecule the desired spatial position in this manner.
Aside from orientation by surface geometry, physical and chemical interactions between the substrate surface and the LC cannot be excluded. Their controlling effect on the orientation of the LC cannot, however, be determined accurately in advance, as was noted by T. Uchida et al. in Mol. Cryst. Liq. Cryst. 60 (1980) 37-52.